Transfer members usually in the form of rollers are commonly used in many industries for applying or transferring a coat or covering to a substrate. For example, rollers are used to apply organic liquid solutions or dispersions of all kinds such as paint, ink, adhesives, hot melts, etc., to various surfaces for decorative or protective purposes. Still other types of application may be effected by rollers, such as the application of an imitation or simulation wood graining to metal surfaces.
Ink transfer members of this type, especially printer's rollers, graining rollers, etc., require a peculiar combination of properties and are subject to severe use. One problem that has long plagued the use of transfer members is their susceptibility to the solvating action of organic solvents, such as benzene, toluol, acetone, and the like, which constantly contact and spread over the member. Under these circumstances, the hardness of the member increases during use because solvents leach away those components which keep the transfer member at a relatively durometer. The organic solvents may also attack a roller causing it to swell out of true and still otherwise destroy its useful physical properties. Wash-up fluids can be the worst offenders. Presses equipped with automatic wash-up features have to operate quickly and so use strong solvents.
One roller used in the printing industry is prepared from a composition of animal glue or such glue modified with glycerine. Rollers of this type, however, have certain disadvantages in that they are vulnerable to atmospheric conditions and to the action of ingredients contained in commercially used inks such as the described solvents. Rollers of this type are also quite hygroscopic and tend to absorb moisture and swell when the humidity is high. Further, in warm weather, the glue compositions become warm and flexible while, conversely, in cold weather they tend to become hard. The glue-glycerine rollers are relatively inexpensive but often have to be re-cast or re-surfaced because of their tendency to change in hardness, crack, and at times disintegrate during use.
Various substitutes have been proposed, such as rubber and vulcanized oil compositions. However, these materials are also quite susceptible to the action of oils and solvents in inks and the like. Rubber rollers especially are apt to swell. Moreover when these rollers dry, they are not only harder but shrink in size.
In order to impart some dimensional stability to ink transfer rollers, blankets, and the like, it has been proposed to use stronger and harder resins from which to form such transfer members, for example, synthetic resins having a Shore A hardness of about 75 to 90. However, such resins are not tacky and have a smooth, shiny surface, such that the ink transfer or ink carrying qualities are seriously adversely affected. On the other hand, if softer, more resilient resins are used, the transfer member is subject to undesired stretching and distortion which can force it out of true. Synthetic rubber inking transfer members which have tended to replace glue glycerine transfer members in modern high-speed presses are more stable but are inadequate for other reasons. For example, some polyurethanes have a tendency to depolymerize in use. Copolymers of butadiene and acrylonitrile harden and crack on exposure to oxygen.
Another type of inking roller in use has a surface formed of a polyester-based polyurethane. Such rollers are useful with hydrocarbon-based inks but have the disadvantage of being readily penetrable by vegetable oil inks which are commonly used in lithographic processes. Due to such penetration, a film of ink forms on the roller surface which creates a residual color-carryover problem, since any future printing is done on a film of ink rather than on the roller surface.
Rollers of the type last described have also been found to be quite susceptible to the action of certain solvents, such as the toluol solvents, that are used in graining inks and also swell due to contact with such solvents. Further, such polyurethanes have a tendency to revert to the liquid state unless an inhibiting agent is incorporated. Use of such an agent increases the cost and complicates the manufacture of the ink-transfer member.
In more recent years a hard rubber has been used in forming inking rollers and the like. While such hard rubber inking rollers have certain advantages, they still leave much to be desired. In particular, hard rubber transfer members have a limited life due to mechanical damage, swelling due to adsorption of an ink vehicle or organic solvent, and the development on the surface of a glaze which causes stripping. It is often necessary to clean such rollers every week or even more frequently.
My prior U.S. Pat. No. 2,538,751 discloses an inking roller of the glue-based type having a surface layer formed from a polyalkylene polysulfide synthetic resin containing an extender.
My prior U.S. Pat. No. 2,598,167 discloses a roller having a surface of animal glue and a central body of vesicular, similar animal glue and a softening material.
My prior U.S. Pat. No. 3,387,074 discloses a process for preparing an ink transfer member such as a printer's blanket from a liquid polyurethane reaction mix by the use of a sheet backing member which is subsequently removed to form the member.
My prior U.S. Pat. No. 3,475,803 discloses a roller for applying ink and the like comprising a layer of resilient cellular material and an outer surface of polyurethane overlying and surrounding the cellular material. The polyurethane is formed from the reaction of a polyethylene glycol, a polyol cross-linking agent, and an isocyanate.
U.S. Pat. No. 3,724,047 to Peterson discloses a polyurethane inking sleeve for a printing roller body which is made by mixing millable, curable polyurethane, a curing agent, plasticizer and fillers and then forming a sheet from the mixture. The sheet is overwrapped about a suitable mandrel and then cured after which the resultant structure is shaped by grinding to provide a tube of uniform wall thickness.